Hyperledger Indy basic concepts

I am reading the Indy walkthrough:

https://github.com/hyperledger/indy-sdk/blob/master/docs/getting-started/indy-walkthrough.md

and I am trying to figure out what is the Indy nodes pool?

And conceptually what is a pool?

And when we talk about Sovrin network which is the relationship between network, Sovrin pool, nodes, and ledger?

• Indy node is application running on the machines participating in a Hyperledger Indy network.
• Indy nodes pool is just an interconnected network of Indy nodes. This commonly refers Hyperledger Indy network you can run in docker for example. Network of Indy nodes is maintaining the state of ledger, verifying transactions.
• Sovrin network is particular instance of Hyperledger Indy network. You can browse transactions on Sovrin network here. Note there's multiple Sovrin networks such as MainNet, TestNet, BuilderNet.